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The return of colder weather and the massive snowstorm that buried portions of the Mid-Atlantic and New England region in the February 11-12 period heralded winter’s resurgence. On January 25, I noted, “All said, February looks to be snowier than normal from at least Washington, DC to Boston. There is some potential that it could be special in terms of snowfall…”
Already, February 2006 ranks as the second snowiest February on record and sixth snowiest month on record for New York City:
1. March 1896: 30.5”
2. December 1947: 29.6”
3. February 1934: 27.9”
4. January 1925: 27.4”
5. December 1872: 27.0”
6. February 2006: 26.9”
Should Boston receive 6.4” more snow, February 2006 would be rank 15th in terms of February snowfall. Such additional snowfall is within the realm of possibility:
Teleconnection Indices:
If one examines the ensemble forecasts for the major teleconnections, a NAO+/PNA- setup appears likely to develop. Such a configuration is actually quite favorable for moderate to large snowfalls in the second half of February in the Middle Atlantic region and accounts for a moderate to high percentage of days with such snowfall:
Days with Snowfall of 2” or More (February 16-29):
Boston: 27%
New York City: 27%
Philadelphia: 40%
Washington, DC (DCA): 39%
Days with Snowfall of 4” or More (February 16-29):
Boston: 26%
New York City: 38%
Philadelphia: 38%
Washington, DC (DCA): 50%
The February 1979 and February 2003 President’s Day snowstorms were the largest such storms to occur under such a setup.
NCEP Ensemble Mean 500 mb Anomalies/CDC’s Experimental Ensembles:
The ensemble means, which proved instrumental in highlighting what became a historic snowstorm for parts of the northern Mid-Atlantic and southern New England region, continue to point to the development of a classic overrunning pattern. They have been extremely consistent toward such a pattern evolution with only a small difference in terms of timing:
NCEP Ensembles: February 14, 2006 0z: 168 Hours:
CDC’s Experimental Ensembles: February 14, 2006 0z: 168 Hours:
NCEP Ensembles: February 6, 2006 0z: 312 Hours:
February 8, 1994:
Through much of the remainder of February, the southern branch of the jet stream should remain fairly active. Hence, there should be readily available moisture for overrunning events and, in terms of timing, the February 20-22 period might offer the highest probability of such an event.
In my view, the southern New England and Middle Atlantic regions, particularly from Washington, DC to Boston will likely see at least an additional moderate to perhaps large snowfall before February is finished. It would not surprise me if some of these cities see 4” or more from a single storm. Incorporating the latest ENSO data into seasons similar to the current one, March looks to see a continuation of above normal snowfall. Weak La Niña-PDO+ winters tend to see above normal to excessive snowfall in the East. With the PDO now having moved solidly into positive territory, such a long-term pattern has unfolded.
In terms of temperatures, after a brief period with above- to much-above normal readings that will peak on February 16, a dramatically colder air mass will blast into the East. Ahead of that air mass temperatures could reach the 50s in southern New England and possibly surpass 60° from Richmond to Philadelphia. On Sunday, readings will likely stay below 30° in Philadelphia, New York City, Providence, and Boston. Low temperatures could fall into the teens there and some single digits Boston and Providence should not be ruled out.
Below normal readings will likely persist from Richmond northward until February 23 +/- 1 day. Then, a gradual warmup, which will be slowest in New England, should develop. By the closing 2-3 days of February, readings in the East could be running somewhat above normal.
After about February 20, the ensembles point to a teleconnections setup whereby the NAO would fluctuate in a +0.50 to +1.50 range while the PNA would remain generally in a 0.00 to -2.00 band. Such a situation has seen two large snowfalls: February 1972 and February 2003 Kocin-Uccellini storms. However, readings during that timeframe are generally moderate to mild (1950-2004 data):
Boston: 35.7° vs. 33.0° for all days 2/16-29 in the 1950-2004 period
New York City: 39.7° vs. 36.6° for all days 2/16-29 in the 1950-2004 period
Philadelphia: 39.5° vs. 36.8° for all days 2/16-29 in the 1950-2004 period
Washington, DC: 43.3° vs. 40.6° for all days 2/16-29 in the 1950-2004 period
Given that the EPO is forecast to remain negative through the rest of the month, readings will probably be cooler than the averages that are implied above. CDC’s experimental ensembles show greater persistence in the cold.
The major idea is that readings will slowly trend toward normal and then possibly somewhat above normal in the closing days of the month.
The idea of a warming trend after February 25 is also supported by the longer-range GSM and RSM models.
Summary:
∙ After an unseasonably warm start on February 16, the overall February 16-22 period should see readings average below normal to perhaps much below normal in the East (particularly from Richmond northward).
∙ February 19 could see high temperatures remain below 30° in Philadelphia, New York City, Providence, and Boston with lows in the teens. A possible low of < 10° is possible in Providence and Boston on either February 19 or February 20.
∙ The February 23-28 timeframe will see readings trend to normal and then possibly somewhat above normal at the end of the month. The warmup will take longest to occur in New England.
∙ Opportunities for overrunning events will be present. One or more cities in the Washington, DC to Boston region could see an event with 4” or more snow and all of these cities should pick up additional accumulations before the end of February.
Pacific Northwest:
Winter is finally returning to the warmth-scorched Pacific Northwest. With a trough likely to predominate in the Pacific Northwest, below normal to occasionally much below normal readings are likely through much of the remainder of February. Overall, I believe the February 16-28 period will see readings average below normal, particularly in the February 16-25 timeframe. During that period, Seattle might well experience one or more days with a low temperature below 25°. The best chance of this cold would probably lie in the February 16-19 period.
The cold is well supported both by the latest computer guidance, ensembles/experimental ensembles, and the longer-range GSM and RSM models.
As noted above, the NAO-PNA are forecast by the ensembles to fluctuate with ranges of +0.50 to +1.50 and 0.00 to -2.00 starting around February 20. In 30% cases, such a setup saw snowfall in 10 days or less. Given an active southern jet, there may well be one or more opportunities for the Pacific Northwest, including Seattle, to see some snow on or after February 20. Some accumulation might even occur.
